In order to optimise the extraction of energy from the wind, wind turbines are typically equipped with a number of sensor devices, which may provide feedback to the control systems of the turbine. For example, sensor devices are commonly used for monitoring environmental conditions at the wind turbine as well as for measuring parameters of the wind turbine components, such as strain. Using the data obtained from these sensor devices, the wind turbine may be operated accordingly, such as controlling the pitch of the blades. Also the yaw of the nacelle, can be adjusted in order to make the wind turbine as efficient as possible at generating energy.
Sensor devices are also commonly used to monitor the condition of the wind turbine components so that damage to the component, or deterioration in the condition of the component can be detected and the necessary maintenance carried out as early as possible. This helps to improve the lifetime of the components and prevents premature or complete failure of the wind turbine. In addition, since certain types of damage can adversely affect the operation of the wind turbine, effective maintenance of the wind turbine components ensures that the wind turbine can operate as efficiently as possible. Such sensor systems are particularly important for wind turbines located in remote areas, such a offshore, coastal or elevated areas, where the time and cost associated with maintenance are relatively high.
Due to the height of most wind turbines, damage from lightning strikes is a recurring operational problem. The use of lightning conductors provides one way of drawing the energy from a lightning strike safely away from the struck component, which as a result may suffer minimal or no damage. However, lightning conductors will not always adequately protect sensor equipment mounted on or in wind turbine components. Sensor systems incorporating metallic components such as wiring and circuits are particularly susceptible to damage from an electrical discharge.
Additionally, the operation of sensor systems in a wind turbine may be adversely affected by the magnetic and electrical fields associated with heavy electrical and mechanical machinery present, for example in the nacelle. As a result, the sensor systems are not able to work in an optimal way.
For these reasons, it is generally preferred to reduce the number of electronic components used in sensor systems and to use optical elements where possible.
One type of sensor which has proved to be sensitive to EMC disturbance from heavy machinery in a wind turbine, such as the generator, are electrical microphones which may be used in acoustic sensors to monitor the condition of wind turbine components based on the sound emissions. It has therefore been previously proposed to use ‘optical’ microphones for sensor applications in wind turbines. Optical microphones detect air movements using a membrane which transfers any oscillations to a beam of light rather than an electrical signal.
For example, it has been previously proposed to provide wind turbines with sensor systems incorporating one or more optical microphones for detecting turbulence in the air flow at the wind turbine. In one proposed system, turbulence sensors are used for the detection of the accumulation of unwanted matter, such as ice or dirt, on the surface of the wind turbine blades. In another proposed application, similar turbulence sensors are used as part of a control system that controls an aerodynamic parameter of a wind turbine blade, such as pitch angle, based on turbulence measurements. Optical microphones have also been proposed for use in place of electrical microphones for detecting vibrations as part of a Condition Monitoring System for monitoring the generator or other equipment within the nacelle.
The known optical microphones have not typically performed as well as traditional electrical microphones, in particular, due to sensitivity of the microphone to movements of the associated optical fibres, which causes false signals to be generated. This problem is particularly serious in moving or rotating structures, such as wind turbines. The performance of many optical microphones is also adversely affected by the fact that the optical sensor must be attached to the sensor membrane, for example in the case of a Fibre Bragg Grating sensor. The membrane therefore becomes heavier and is not free to respond accurately to air movements. In addition, in existing arrangements for optical microphones, the required light generation and detection apparatus is relatively expensive, so that it is not economically feasible to use such systems on a commercial scale.
It would therefore be desirable to provide a sensor system incorporating a novel optical microphone arrangement, which has an improved performance and which overcomes the problems associated with existing optical microphones. It would be particularly desirable if such a system could be formed from relatively robust and low cost components such that the system is more economically feasible for use in wind farms. It would further be desirable if such a system could be readily adapted for a variety of different sensor applications on a wind turbine.
According to the present invention there is provided a wind turbine including an optical sensor system comprising one or more optical sensors, each sensor comprising: a reflective sensor membrane; a light source for illuminating a surface of the sensor membrane; an optical dispersive element arranged to disperse the light beam from the light source; and a light detector for receiving a portion of the light beam after reflection from the surface of the sensor membrane and after dispersion of the light beam by the optical dispersive element. The wavelength of the light received at the light detector varies as a function of the displacement of the sensor membrane and the light detector operatively provides an output based on changes in the wavelength of the received light. The wind turbine further comprises a controller for receiving data from the sensor system and based on the received data controlling an operating parameter of the wind turbine.
The term ‘operating parameter’ refers to any parameter of the wind turbine which affects the operation of the wind turbine. The parameter to be controlled based on the data received from the optical sensor system will depend upon the function of the sensor system and examples will be described below. In certain embodiments, the operating parameter to be controlled may be an aerodynamic parameter of the wind turbine blade, such as pitch or rotor rpm. In other embodiments, the operating parameter to be controlled may be a parameter of the generator, such as load, power or rpm.